Seals for sealing off annular gaps are required in technology in particular in mechanical engineering in the most widely varying geometrical and utilitarian shapes. Consequently the most widely varying structural configurations of such seals are known in the state of the art—including in the form of prepared standard components, even to a standardized configuration. One of the simplest forms of known annular seals is the O-ring made of rubber. Something that is of a substantially more complicated structure is for example what is known as the shaft sealing ring, a sealing element comprising a metal ring as the outer seat and a radially inwardly facing sealing lip made of rubber. Shaft sealing rings of that kind serve for example for sealing a transmission housing from which a rotating shaft is extended. For that purpose the metal ring is fitted in the bore in the housing through which the shaft is passed, and the sealing lip bears against a circular-cylindrical peripheral surface, which is as smooth-walled as possible, of the shaft. The contact surface area between the sealing lip and the surface of the shaft is reduced to an annular line around the shaft, more specifically by virtue of the fact that the sealing lip tapers radially inwardly to a geometrically sharp edge. That design configuration permits high speeds of rotation for the shaft, in which case for example transmission oil which is in the interior of the housing and which is to be prevented from escaping from the housing by the seal forms a film of lubricant under the sealing lip. As is known dynamic pressure conditions in the region of the contact surface then provide that the oil does not penetrate outwardly through beneath the sealing lip. In addition, in particular felt rings are known for sealing off annular gaps around a component which not only rotates but which is also moved through the bore with a translatory motion.
At any event seals are exposed to wear and possible destruction for example due to fouling or pressure—in the form of seals sealing against a moving component but in particular also by virtue of abrasive wear and fatigue—, and that can generally also result in erosion of the sealing element in the region of the contact surface and thus can result on the one hand in a reduction in a biasing force with which the seal bears against a complementary component, and on the other hand can even result in the seal opening up and gaping open. Therefore wear of the seal restricts the operating life thereof and makes it necessary to replace the seal when the apparatus of which the seal is a component part has a longer service life.
DE-OS No 2 144 681 discloses a composite seal for piston rods and the like. The seal has a first annular member and a second annular member which are arranged in a condition of butting against each other in the axial direction and fixedly around the outside of a reciprocatable member, wherein the first and second annular members have portions which are in sealing engagement with the reciprocatable member. The second annular member, the high-pressure member, is loaded by the first annular member in order to increase the bearing pressure of the high-pressure member or the lip thereof against the reciprocatable member.
U.S. Pat. No. 4,201,392 discloses a seal which is made up of three parts.